Non riesco a far funzionare la SEO URL sul forum phpBB 3 che ho appena istallato... come faccio?

Codice HTML:

# Lines That should already be in your .htacess
<Files "config.php">
Order Allow,Deny
Deny from All
</Files>
<Files "common.php">
Order Allow,Deny
Deny from All
</Files>

# You may need to un-comment the following lines
# Options +FollowSymlinks
# To make sure that rewritten dir or file (/|.html) will not load dir.php in case it exist
# Options -MultiViews
# REMEBER YOU ONLY NEED TO STARD MOD REWRITE ONCE
RewriteEngine On
# Uncomment the statement below if you want to make use of
# HTTP authentication and it does not already work.
# This could be required if you are for example using PHP via Apache CGI.
# RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]
# REWRITE BASE
RewriteBase /forum/
# HERE IS A GOOD PLACE TO FORCE CANONICAL DOMAIN
# Define fully qualified ssl aware protocol
# RewriteCond %{SERVER_PORT}s ^(443(s)|[0-9]+s)$
# RewriteRule ^.*$ - [env=HttpFullProto:http%2://]
# RewriteCond %{HTTP_HOST} !^pcresource\.altervista\.org$ [NC]
# RewriteRule ^(.*)$ %{ENV:HttpFullProto}pcresource.altervista.org/forum/$1 [QSA,L,R=301]

# DO NOT GO FURTHER IF THE REQUESTED FILE / DIR DOES EXISTS
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
#####################################################
# PHPBB SEO REWRITE RULES ALL MODES
#####################################################
# AUTHOR : dcz www.phpbb-seo.com
# STARTED : 01/2006
#################################
# FORUMS PAGES
###############
# FORUM INDEX REWRITERULE WOULD STAND HERE IF USED. "forum" REQUIRES TO BE SET AS FORUM INDEX
# RewriteRule ^/forum\.html$ index.php [QSA,L,NC]
# FORUM ALL MODES
RewriteRule ^/(forum|[a-z0-9_-]*-f)([0-9]+)(-([0-9]+))?\.html$ viewforum.php?f=$2&start=$4 [QSA,L,NC]
# TOPIC WITH VIRTUAL FOLDER ALL MODES
RewriteRule ^/(forum|[a-z0-9_-]*-f)([0-9]+)/(topic|[a-z0-9_-]*-t)([0-9]+)(-([0-9]+))?\.html$ viewtopic.php?f=$2&t=$4&start=$6 [QSA,L,NC]
# TOPIC WITHOUT FORUM ID & DELIM ALL MODES
RewriteRule ^/([a-z0-9_-]*)/?(topic|[a-z0-9_-]*-t)([0-9]+)(-([0-9]+))?\.html$ viewtopic.php?forum_uri=$1&t=$3&start=$5 [QSA,L,NC]
# PHPBB FILES ALL MODES
RewriteRule ^/resources/[a-z0-9_-]+/(thumb/)?([0-9]+)$ download/file.php?id=$2&t=$1 [QSA,L,NC]
# PROFILES ALL MODES WITH ID
RewriteRule ^/(member|[a-z0-9_-]*-u)([0-9]+)\.html$ memberlist.php?mode=viewprofile&u=$2 [QSA,L,NC]
# USER MESSAGES ALL MODES WITH ID
RewriteRule ^/(member|[a-z0-9_-]*-u)([0-9]+)-(topics|posts)(-([0-9]+))?\.html$ search.php?author_id=$2&sr=$3&start=$5 [QSA,L,NC]
# GROUPS ALL MODES
RewriteRule ^/(group|[a-z0-9_-]*-g)([0-9]+)(-([0-9]+))?\.html$ memberlist.php?mode=group&g=$2&start=$4 [QSA,L,NC]
# POST
RewriteRule ^/post([0-9]+)\.html$ viewtopic.php?p=$1 [QSA,L,NC]
# ACTIVE TOPICS
RewriteRule ^/active-topics(-([0-9]+))?\.html$ search.php?search_id=active_topics&start=$2&sr=topics [QSA,L,NC]
# UNANSWERED TOPICS
RewriteRule ^/unanswered(-([0-9]+))?\.html$ search.php?search_id=unanswered&start=$2&sr=topics [QSA,L,NC]
# NEW POSTS
RewriteRule ^/newposts(-([0-9]+))?\.html$ search.php?search_id=newposts&start=$2&sr=topics [QSA,L,NC]
# UNREAD POSTS
RewriteRule ^/unreadposts(-([0-9]+))?\.html$ search.php?search_id=unreadposts&start=$2 [QSA,L,NC]
# THE TEAM
RewriteRule ^/the-team\.html$ memberlist.php?mode=leaders [QSA,L,NC]
# HERE IS A GOOD PLACE TO ADD OTHER PHPBB RELATED REWRITERULES

# FORUM WITHOUT ID & DELIM ALL MODES
# THESE FOUR LINES MUST BE LOCATED AT THE END OF YOUR HTACCESS TO WORK PROPERLY
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^/([a-z0-9_-]+)(-([0-9]+))\.html$ viewforum.php?forum_uri=$1&start=$3 [QSA,L,NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^/([a-z0-9_-]+)\.html$ viewforum.php?forum_uri=$1 [QSA,L,NC]
# FIX RELATIVE PATHS : FILES
RewriteRule ^/.+/(style\.php|ucp\.php|mcp\.php|faq\.php|download/file.php)$ $1 [QSA,L,NC,R=301]
# FIX RELATIVE PATHS : IMAGES
RewriteRule ^/.+/(styles/.*|images/.*)/$ $1 [QSA,L,NC,R=301]
# END PHPBB PAGES
#####################################################
il forum risiede qui http://pcresource.altervista.org/forum ma appena si va in una sezione mi da errore